The field of the invention pertains to electroacoustic audio reproduction systems, the most common examples of which are monophonic and stereophonic speaker systems. Best individual speaker or driver performance is severely limited within the normal range of hearing (about 20-20,000 Hz). Acoustic output and efficiency become severely limited outside of the frequency range of best performance. This may be at the upper or lower end of the frequency range depending on the particular driver.
One approach to the problem is U.S. Pat. No. 3,497,621 wherein a low frequency compensation circuit for a single speaker is disclosed. A second compensating circuit for a single speaker is disclosed in U.S. Pat. No. 3,838,216.
A more contemporary approach is to provide multiple separate speakers or drivers to cover the entire range of frequencies. Electronic cross-over or filter networks are utilized to feed low frequencies to low frequency drivers ("woofers") and high frequencies to high frequency drivers ("tweeters"). U.S. Pat. No. 2,802,054 discloses the use of a cross-over network and compensating network for separate low and high frequency speakers. Disclosed in U.S. Pat. No. 3,727,004 is an electronic cross-over or filter network for a multiple speaker system sold commercially. Cross-over or filter circuits incorporating additional passive electronic elements for both two and three speaker systems are disclosed in U.S. Pat. No. 3,838,215. However, despite extensive speaker circuit development, the quest for better speaker performance continues in the attempt to meet the public desire for a more perfect reproduction of sound and in particular music.